Many welding applications such as MIG (metal inert gas) or GMAW (gas metal arc welding) utilize a welding power supply (system) with a wire feeder to provide filler metal to the weld. A welding power supply or system as used herein includes one or more of the following components: a wire feeder, a power source or source of power, a torch or gun, a wire feeder controller, and a power source controller to control the various components (it may also exclude some of these components, such as the power source). The components may be packaged discreetly, or in various combinations. Additionally, the wire feeder controller may be part of, distinct from but cooperates with, or independent of the power source controller.
One prior art welding power supply/wire feeder system includes a Miller XRA or XRW.RTM. wire feeder used in combination with a Miller Delta Weld.RTM. power source. This system has the control panel, including user selectable devices, on the front or control panel of the wire feeder.
Generally, the wire feeder motor will provide wire at a nominally constant speed (typically given in inches per minute) in response to the wire feed speed controller. The power source welding output is likewise responsive to the welding power source controller. The controllers have user selectable devices to allow the user to set parameters such as weld wire feed speed, weld current, weld voltage, and run-in wire feed speed. The input devices are typically potentiometers mounted on the control panel of the system or wire feeder, but may include other user selectable input devices, including digital devices. The user sets the parameters, and then pulls a trigger on a torch to begin welding. The trigger activates the wire feeder, causing it to feed wire. The trigger also activates the source of power, causing it to provide output power (often by closing a relay or contactor).
Wire feed welding power supplies are used for a variety of processes, including spot or tack welding, and continuous welding. Some applications use both processes.
For example, when assembling a truck frame or other large object, the welder will often spot weld around the edge of the frame to tack the frame together, and then fill in with a continuous weld. Welding power supplies often come with many feet (30, 50 or 100 or more) of welding cable to accommodate welding various sides of such large objects.
The power supply or system can then be left on one side of the object to be welded, and the welder can pass the torch cable around or underneath, and weld the opposite side without moving the power supply or system.
Tack welding is performed by periodic activation of the source of power and wire feeder, to weld in a specific location. Activation is typically accomplished by pulling a trigger on the torch. The trigger is released when the spot or tack weld is completed, and the source of power shuts down and wire feeder stops.
Continuous welding is accomplished by pulling the trigger, and the power source provides power and/or the wire feeder feeds wire, so long as the trigger remains pulled. Some prior art systems included a trigger hold or latch feature. With this feature, pulling the trigger latches the power supply or system on until the trigger is retriggered.
There are a variety of prior art trigger hold implementations. One is a simple design which automatically latches or unlatches each time it is pulled. This type of prior art system typically uses an alternating relay, or its electronic equivalent, and the circuit merely provides that the first trigger closure initiates the welding operation, and the second trigger closure will terminate it. One disadvantage of this type of system is that the operator could walk away from the system before terminated welding operation, and the system would continue to operate.
Similarly, an inadvertent triggering, such as a person bumping the trigger, could also cause the system to be initiated. This may be dangerous and will likely cause an undesirable amount of wire to be fed before shutting down by retriggering.
Another type of trigger hold system relies on a current sensing relay to latch the system in operation. However, this requires that the arc be terminated in order to stop the wire feeding, which often results in too much wire being drawn from the tip of the torch when the operator pulls the torch away from the workpiece to extinguish the arc.
The Miller 50 M Intellmatic.RTM. wire feeder had a nonstandard option that included a trigger latch which was set by pulling the trigger, and then releasing the trigger prior to the expiration of period of time. If the trigger was not released within the period of time then the latch was not set, and continuous welding was performed manually.
A trigger hold system described in U.S. Pat. No. 4,531,045 combines the three previously described systems by requiring the welder to pull a trigger, hold the trigger pulled until current flow was established, and then within one second of the initiation of current flowing, release the trigger to set the latch. The latch is removed by retriggering. After a two second delay the system may be turned on again by another trigger.
These prior art trigger hold schemes are designed for only continuous welding, and each does not work well for spot welding applications. Each will cause the latch to be set when tack welding (because the time to weld the tack will likely be less than the threshold). Thus, to stop the tack weld the trigger would have to be retriggered, often resulting in excess wire feeding for the tack weld.
Some prior art systems attempted to overcome this disadvantage by providing a toggle switch on the control panel that allowed the user to select between the trigger hold mode, and a non-hold mode (useful for spot welding).
Unfortunately, for applications where the welder is some distance from the control panel (such as welding on a truck frame or the opposite side of another large object) it is not convenient for the welder to switch between spot or tack welding and continuous welding.
Accordingly, a trigger hold that is useful for both continuous and tack or spot welding is desirable. Such a trigger hold will preferably be operable by the user, at the torch, and will cause the system to latch on for continuous welding, but will not cause the system to latch on when tack or spot welding.
Some prior art welding power supply/wire feeder systems allow the user to set to the wire feed speed at the torch. This allowed the user to adjust the wire feed speed, without returning to the control panel. Typically, the torch controller was a pot that allowed the user to select the full range of speeds. One disadvantage of this type of torch control is that the relatively small knob on the torch was used to control the full range of speeds, and it was difficult for the user to "dial in" the desired speed. Accordingly, a welding wire feed speed control located on the torch, that allows the user to more accurately select the speed is desirable.
Prior art welding power supplies/wire feeders also sometimes include a feature called run-in. Run-in allows the welder to control the speed at which the wire approaches the workpiece prior to the arc forming and welding starting.
Prior art controllers allow the welder to select the run-in speed at any speed over the entire range of wire feed speeds. This, however, is dis-advantageous because it may be difficult to select the proper run-in speed, relative to the wire feed speed during welding. Accordingly, a run-in control that allows the welder to select the wire feed speed during run-in, relative to the wire feed speed during welding is desirable.